This invention relates to a mold using a membrane filter for forming ceramic bodies, a method for forming ceramic bodies by the use of the mold and/or a pressure casting molding method for ceramic bodies by means of a hydrophobic medium.
Molds made of plaster, synthetic resins, ceramics and the like have been known for forming inorganic materials such as ceramic materials and the like into predetermined shapes by means of potters wheels or by casting, wet press forming and the like. Such molds generally have a permeability to remove a solvent medium included in a forming body (slurry) of the inorganic material such as a ceramic material. Dewatering and mold release of a molded body are effected by suction or pressurizing. In other cases, the dewatering and mold release are effected by congregating particles of the blank material with the aid of ion exchange between ions in the mold and the slurry at surfaces of the mold.
Recently, a forming mold has been proposed which is of a two layered construction consisting of an outer layer having coarse pores and an inner layer having fine pores in order to prevent blank material particles from entering the mold to prevent the mold from being clogged and to improve the dewatering efficiency (Japanese Patent Application Publication No. 14,451/81).
In recent years, the pressure casting molding method has been noticed. With such a pressure casting method, as shown in FIGS. 1 and 2 a ceramic slurry 25 is poured through a pouring portion 22 into a mold 27 having a required inner cavity and the poured slurry 25 in the cavity is pressurized by a gas such as air introduced through the pouring portion 22 to remove a solvent medium through a permeable mold 23 at the other end of the mold, thereby obtaining a ceramic molded body of a high density.
However, these molds of the prior art have the following disadvantages. The plaster mold is poor in mechanical strength and therefore the mold can be repeatedly used only very few times. Moreover, the mold of a synthetic resin or a ceramic material is likely to be clogged every time when it is used and therefore cleaning of the mold is required. As the number of times the mold is used increases, the time required for casting is progressively increased, thus lowering the moldability of the material. Further, as it is difficult to obtain desired fine pores, the time required for casting is different for each mold so that control of a number of molds is difficult.
On the other hand, with the mold consisting of two layers, these layers are substantially integrally formed, so that the clogging of pores is not eliminated. Moreover, as the number of times the mold is used increases, the moldability decreases.
Furthermore, with the pressure casting of the prior art above described, the cast slurry is directly pressurized by air, gas and the like, so that when the pressure is higher than 10 kg/cm.sup.2, the use of the mold is limited by high pressure gas regulation and there is a large risk of explosion or the like. Accordingly, this kind of the mold is difficult to use.
In order to simplify the release of a molded body from the impermeable mold or to simplify the release of the molded body from the permeable mold after removal of a solvent medium, surfaces of the impermeable or permeable mold in contact with a ceramic slurry are previously coated with a mold release agent. However, the mold release agent is extended through the permeable mold by pressurizing or by pressurizing and sucking in pressure casting, so that the release of the molded body from the impermeable or permeable mold becomes difficult. The release of the molded body often becomes more difficult dependent upon the shape and size of the molded body.
Moreover, when the slurry is pressurized by the air through the pouring portion to remove the solvent medium through the permeable mold, the air passes through parts of boundary surfaces between the impermeable or permeable mold and the molded body which is about to complete its molding. Therefore, the parts of the boundary surfaces are locally promptly dried so that cracks tend to occur in these parts.